Processes for converting liquefied starch to a mixture of fructose and glucose are well known in the art. Generally, these processes involve treating the starch with glucoamylase to obtain a product with a high glucose content and then treating such a product with glucose isomerase to convert a portion of the glucose to fructose.
Exemplary of processes for converting starch with enzyme systems comprising more than one enzyme are those taught by Hurst in U.S. Pat. No. 3,897,305 wherein liquefied starch is treated with soluble glucoamylase and pullulanase and by Hebeda et al. in U.S. Pat. No. 3,922,201 wherein ungelatinized starch is treated with a system comprising soluble alpha-amylase, glucoamylase and glucose isomerase.
A number of immobilized enzyme systems have been disclosed in the art. G. T. Tsao (Enzyme Technology Digest, Vol. 1, No. 2, Nov. 1972) and P. I. Y. Y. Lee (Enzyme Technology Digest, Vol. 2, No. 1 July 1973) reported certain proposals for the simultaneous utilization of immobilized glucose isomerase and glucoamylase. G. K. Lee presented a paper dealing with the joint use of immobilized glucoamylase and glucose isomerase in a mixed bed reactor (Iowa State University Immobilized Enzyme Meeting, Ames, Iowa, January 1975).
Y. Y. Lee et al. in Final Grant Report NSF GI-34933, June 1973 and P. J. Reilly in Final Report for NSF RANN Grant ER 772-03492, ERI-76077, October 1975, disclosed various immobilized enzyme systems. Y. Takasaki, in Japanese Patent NS 16654/72 reported the joint use of glucoamylase and glucose isomerase in both soluble and immobilized forms to convert liquefied starch to a glucose-fructose mixture. German Patent 2,404,101 also discloses the combined use of glucoamylase and glucose isomerase.
Hollo et al., Die Starke, Vol. 27, No. 7, pp. 232-35, 1975, teaches the utilization of immobilized glucose isomerase and glucoamylase in alternate beds to convert liquefied starch to a 96 D.E. product. German Pat. No. 2,441,255 discloses the use of a combination of immobilized beta-amylase and pullulanase for the conversion of liquefied starch to a high maltose syrup.